Introduction: Skeletal muscle atrophy and weakness affect older adults and often lead to frailty, falls, fractures, immobility and institutionalization. At any age this decline can be ameliorated by progressive resistance training (PRT). During traditional PRT with weights, the agonist (target) muscles lift a weight with a shortening contraction (SC) and then lower the same weight with a lengthening contraction (LC). Recent randomized controlled trials suggest that eliminating the SC-phase and applying a larger-than-normal load to the agonist muscles during the LC-phase of the training cycle (LC-only training) can result in greater strength increases at a lower acute metabolic cost and a lower rate of perceived exertion than traditional SC-LC training. LC-only training, however, tends to be more specific to improving LC strength than SC strength. Even larger increases in both SC and LC dynamic strength and muscle morphology are achieved by combining lower-load SC with higher-load LC training which is particularly attractive for older and energetically impaired adults. Despite the advantages and need for such a regimen, no commercial system exists that has the flexibility to enable both lower-load SC and higher-load LC training that is suitable for older adults and accessible to the broader public for independent use. Innovation: Bio Logic Engineering Inc. is addressing this need by developing an innovative computer controlled and motorized system that enables safe and effective strength training with velocity-controlled shortening contraction (VSC) and lengthening contraction (VLC) training protocols. The system provides programmable variable-resistance force target trajectories across the range-of-motion in both VSC and VLC phases of each training repetition. Trainees modulate their level of exertion to follow customized target trajectories that are visually displayed along with real-time force-position feedback. The unique design is ideally suited for older adults since the magnitude (intensity) of the target trajectory for the VLC phase can be programmed to be significantly elevated with respect to the VSC phase. The technology is currently being developed as a leg press machine to improve mobility in older adults but is transferable to training of other muscle groups. Aims of Phase II: System mechanics, electronics and software will be refined to improve safety, ease-of-use, flexibility and dynamic performance. Clinical performance will be assessed with 36 healthy older adults randomized into two different 16-week PRT groups stratified by gender: (GROUP 1) 9 males and 9 females will perform traditional SC-LC training with the weight-stack and (GROUP 2) 9 males and 9 females will perform motor-driven VSC-VLC training. The hypothesis to be tested is: the adaptive response to 16-weeks of PRT will be greater for the VSC-VLC group than the SC-LC group as measured by the maximum voluntary leg extension strength during standard one-repetition maximum SCs, one-repetition maximum VSCs, and isometric contractions. Commercial Opportunity: The potential market for the system is large considering its use in health clubs, wellness centers, physical therapy clinics, assisted-living communities, hospitals, and academic institutions. The objective of this research is to continue to develop, refine and test a novel computer-controlled strength training system to assist in combating sarcopenia which is an age-related progressive loss of skeletal muscle that leads to a decline in muscular strength, power and mobility. The working hypothesis is that 16 weeks of progressive resistance training with the new computer-controlled system, which enables variable-resistance through the range-of-motion and elevated loading during the muscle lengthening phase, will lead older adults to greater increases in strength than with traditional weight training methods. The long-term goal of this research is to make widely available an innovative apparatus and method to improve the efficacy of progressive resistance strength training, especially in older adults. [unreadable] [unreadable] [unreadable] [unreadable]